1. Field of the Invention
This invention relates to radio receivers, and more particularly, radio receivers capable of simultaneously receiving content broadcast on analog and digital broadcast channels.
2. Description of the Related Art
In recent years, digital radio has emerged as an alternative to analog-only radio broadcasting. For example, the introduction of what was originally known as hybrid digital radio (hereinafter “HD radio”) enabled radio programming to be broadcast in both analog and digital formats. Furthermore, the programming may be simultaneously broadcast (sometimes referred to as “simulcast”) in both analog and digital formats. Radio receivers may be designed to receive both of these formats, and may utilize the analog data or the digital data based on various factors.
In one example of an HD radio simulcast, an audio program may be transmitted in analog format on an FM (frequency modulated) carrier signal. The audio program may be simultaneously broadcast in digital format in sidebands occurring on either side of the FM signal. The digital format may include a number of subcarriers modulated using quadrature phase shift keying (QPSK) and multiplexed using orthogonal frequency division multiplexing (OFDM). Often times, the HD radio receiver will first acquire the FM signal and subsequently, the digital signal. Audio may begin playing on the receiver using data extracted from the FM signal. A blend operation may then be performed to blend audio extracted from the FM signal with audio extracted from the digital signal. At the end of the blend process, the audio playback may be entirely based on the digital signal, unless the digital signal fades. Should the digital signal fade, then the analog signal may be used as a backup mechanism for continuing to receive the programming. Should the digital signal be re-acquired, the blend operation may be repeated.
In the above example, the delay between the analog and digital signals may be inherent due to the multi-second processing delay required for transmission of OFDM signals. Accordingly, broadcasters of HD radio content may delay to the transmission of the analog FM signal by a static amount of time in order to align the analog and digital signals at the receiver.